(1) Field of the Invention
The present invention relates to an electrodeless discharge lamp that does not include an electrode inside its discharge vessel.
(2) Related Art
These days have seen an increasing use of electrodeless discharge lamps, because of their excellent energy efficiency and long lifespan. The electrodeless discharge lamps are broadly divided into two types: electrodeless fluorescent lamps and high intensity discharge lamps (H.I.D.). In the following, an electrodeless fluorescent lamp is taken as an example, and the structure thereof is described.
In an electrodeless fluorescent lamp, a discharge vessel is placed to be in the proximity of an induction coil, the induction coil being provided on a circuit substrate in an upright position. The discharge vessel is translucent and in which a discharge gas made of a rare gas and mercury is enclosed, and the circuit substrate is stored inside a case so as to be avoided contact of human hands while the lamp is being used.
In most cases, the discharge vessel and the circuit substrate are both attached to the case. In particular, the discharge vessel is attached to the case, with a layer made of heat-resistance silicone in-between.
The silicone used for attaching the discharge vessel to the case will gradually deteriorate; for the silicone layer is subject to the heat from the discharge vessel, when the lamp emits light. Therefore, since electrodeless fluorescent lamps have a significantly longer lifespan compared to conventional fluorescent lamps that have an electrode in their discharge vessel, it is hard for the silicone layer of electrodeless fluorescent lamps to maintain a bonding strength between the discharge vessel and the case, until the last stage of the lifespan. Accordingly, it sometimes happens that the discharge vessel falls off from the case.
In addition, the electrodeless fluorescent lamp described in the above has a structure in which the discharge vessel is coupled to the induction coil, through the mediation of the circuit substrate, the case, and the like. According to this structure, assembly variations will occur at the time of assembling the parts together, besides the variations of size for individual parts. Accordingly, it sometimes happens that the position between the discharge vessel and the induction coil deviates from as designed. When the relative position between the discharge vessel and the induction coil deviates, the problem arises that the luminous performance differs according to an area of the discharge vessel.
A technology has been proposed by the Japanese Laid-open Patent Application No. H09-320541 for coping with the above mentioned problem. In this patent application, a case is provided with a convex portion that is used to couple the discharge vessel to the case; and a corresponding concave portion is provided on the corresponding area of the discharge vessel. The discharge vessel will be coupled to the case, by fitting the convex portion to the concave portion.
For the electrodeless fluorescent lamp produced using the above technology, the discharge vessel will be prevented from falling off at the later stage of lifespan, and the deviation in relative position between the discharge vessel and the case is reduced to a minimum.
However, in the method of coupling the discharge vessel to the case, in order to fit the convex portion to the concave portion, a force is to be exerted on the discharge vessel and on the case. This means that a force will be exerted on a discharge vessel which is made of glass. For assuring strength and accuracy in mounting the discharge vessel to the case, it becomes necessary to have a smaller clearance between the concave portion and the convex portion, which further increases a force that the discharge vessel is subject to. In some cases, this leads to a break of the discharge vessel or the case.
As mentioned in the above, for the electrodeless fluorescent lamp produced using the disclosed technology, the accuracy in position between the discharge vessel and the case is assured; however, the accuracy in position between the discharge vessel and the induction coil (which is an important factor in assuring the uniform luminous performance throughout the entire luminous area) will not be assured. This is due to the structure of this electrodeless fluorescent lamp, in which its discharge vessel and induction coil are attached to each other, through a mediation such as the circuit substrate and the case. Therefore, the positioning accuracy of the discharge vessel and the induction coil will be hindered, as much as an accumulation of various kinds of deviations yielded at the time of producing and assembling the mediation parts.
Considering the above, it can be said that the disclosed technology is not for practical use.
The object of the present invention, in order to solve the stated problems, is to provide an electrodeless fluorescent lamp whose discharge vessel is prevented from falling off, and that delivers a uniform luminous performance throughout the entire luminous area by assuring an accuracy in position between a discharge vessel and an induction coil.
In order to achieve the above object, the electrodeless discharge lamp of the present invention is characterized by having a translucent discharge vessel in which a discharge gas is enclosed, the discharge vessel having a first coupling member; an induction coil; and a bobbin that includes a coil-holding part and a vessel-mounting part that are formed as a single piece, the vessel-mounting part having a second coupling member, where the coil-holding part holds the induction coil on an outer surface thereof, and is placed in a proximity of the discharge vessel, and the first coupling member and the second coupling member are coupled so as to mount the discharge vessel on the vessel-mounting part of the bobbin.
The electrodeless discharge lamp according to the present invention has a discharge vessel that is mechanically coupled by the second coupling member of the vessel-mounting part. Accordingly, the discharge vessel will be prevented from falling off, over a long period of time.
In addition, in the above-mentioned conventional electrodeless discharge lamp, it is difficult to maintain a positioning accuracy between its discharge vessel and induction coil, since the discharge vessel and the induction coil are coupled to each other, with a plurality of parts in-between. Whereas in the electrodeless discharge lamp of the present invention, the coil-holding part and the vessel-mounting part are formed as a single piece, where the coil-holding part holds the induction coil, and the vessel-mounting part coupling the discharge vessel to the bobbin. According to the above structure, the electrodeless discharge lamp of the present invention realizes a high positioning accuracy between the discharge vessel and the induction coil in the mounting process. At the same time, the relative position between the discharge vessel and the induction coil will not vary, according to a heat generated from the discharge vessel at the time of the lamp being used.
Accordingly, the electrodeless discharge lamp according to the present invention will assure a uniform luminous performance throughout its luminous area, and will not be subject to a damage that would happen due to the induction coil coming in contact with the discharge vessel during the transportation of the lamp, between the shipping of the lamp to the setting thereof, for example.
In the stated electrodeless discharge lamp, it is desirable to have a structure in which one of the first coupling member and the second coupling member is a protrusion, and the other is a groove that is shaped to receive the protrusion is desirable, in order to produce the lamp with ease, and that to mount the discharge vessel with a high positioning accuracy.
In the stated electrodeless discharge lamp, the discharge vessel is desirably coupled to the vessel-mounting part so that the discharge vessel is held in a fixed position, in order to further increase the positioning accuracy between the discharge vessel and the induction coil.
In the stated electrodeless discharge lamp may further have the following structures: a structure in which a distance between a groove bottom and a center of the vessel-mounting part continuously decreases in a diameter direction, the groove bottom being a part of an inner surface of the bottom that is under the groove, and the protrusion of the discharge vessel is guided toward a center of the vessel-mounting part in a diameter direction by being rotated along the groove bottom, so as to eventually hold the discharge vessel in a fixed position; and a structure in which the groove is formed along the inner wall so as to continuously decrease in height, and the protrusion of the discharge vessel is guided toward a height direction of the groove formed on the vessel-mounting part, by being rotated along the part of the inner wall, so as to eventually hold the discharge vessel in a fixed position. These structures are desirable in view of assuring the positioning accuracy between the discharge vessel and the induction coil. These structures are also advantageous in that a large force is not necessary in coupling the discharge vessel.
Here, the discharge vessel may be rotated leftward when the vessel-mounting part is seen from the discharge vessel. This is an opposite direction to the rightward direction in which the lamp is rotated when setting the lamp.
Generally speaking, in taking off the electrodeless discharge lamp at the last stage of its lifespan, the lamp is made to be loose, by rotating the lamp in a leftward direction. Considering the above, it is advantageous to couple the discharge vessel by a leftward rotation, since at the time of taking off the lamp having ended its life through a leftward rotation, the discharge vessel will be further fastened to the vessel-mounting part. This will prevent the discharge vessel from falling off from the vessel-mounting part.
In the above described electrodeless discharge lamp, the discharge vessel may be held in a fixed position, by being directly coupled to the vessel-mounting part, or by means of a member made of a resin material in-between, such as silicone and epoxy.